You can't predict everything. Even when you give yourself extra time, some tasks might take longer than planned. Unexpected events can come up and slow you down. Your bike could break on your way to pick up your sister, or you might misplace the notes you need to finish your homework. It's important to have a schedule and to stick to it whenever you can. It's also important to be flexible when you need to. Be ready to change and adjust your plan so that a small surprise doesn't disrupt your whole day.
According to the passage, you should have a plan...